1. Field of Invention (Technical Field)
The present invention relates to sparging apparatuses and methods of in situ groundwater remediation for removal of dissolved chlorinated hydrocarbons and dissolved hydrocarbon petroleum products. Remediation of saturated soils may also be obtained by employment of the present invention. In particular the present invention employs microporous diffusers injecting duo-gas bubbles into aquifer regions to encourage biodegradation of leachate plumes which contain biodegradable organics, or Criegee decomposition of leachate plumes containing dissolved chlorinated hydrocarbons.
2. Background Prior Art
The introduction of air bubbles into aquifers for the purpose of remediation is a recent advancement in in-situ treatment of groundwater. (Marley, et. al, 1992; Brown et. al., 1991). Contained air entrainment has been used for many years to provide vertical movement of water in low-head aquariums and in the development of public well supplies (Johnson, 1975). Aeration of aquifers for plume management was suggested to accelerate bacterial degradation of dissolved organic compounds (JRB, 1985). As the bubble volume increases in density above re-aeration needs by approaching ratios beyond 1 to 10 (1 water to 10 air), gas transfer begins to dominate. In this case, volatile organics may be physically transported from the saturated aquifer to the overlying unsaturated zone (vadose zone).
There is a well recognized need for a simple test to evaluate a potential site to assist with design of sparging systems deployed on a remediation site. Whereas hydraulic tests have been performed for some period of time based upon the well known Theis equation, the introduction of air bubbles (particularly microscopic bubbles) is new. Also, whereas the introduction of air to the pressure vessel is continuous, the production of bubbles, particularly the microscopic variety, is a discrete discontinuous process. Bubbles, once generated, may take preferential pathways, determined largely by the substratum and secondarily by the introduction of pressure (Ji, et. al., 1993).
Applicant is aware of prior art devices that have used injection of air to facilitate biodegradation of plumes. In U.S. Pat. No. 5,221,159 to Billings shows injection of air into aquifer regions to encourage biodegradation of leachate plumes which contain biodegradable organics together with simultaneous soil vacuum extraction.
Also in U.S. Pat. No. 4,730,672, to Payne, there is disclosed a closed-loop process for removing volatile contaminants. However Payne deals only with volatile contaminants. Payne discloses a withdrawal well is surrounded by multiple injection wells. Pressurized air is injected into the ground water through the injection wells, and is withdrawn under vacuum from the withdrawal well whereupon contaminants are removed from the air stream and the air is then recycled through the system. The U.S. Pat. No. 4,588,506, to Raymond et al., discloses the injection of a diluted solution of hydrogen peroxide into a contaminated soil for enhancing biodegradation of organic contaminants in the soil. Raymond discloses intermittent spiking of the hydrogen peroxide concentration to eliminate biota to increase soil permeability. Raymond has the disadvantage of failing to deliver of oxygen throughout the system, and depends on a complicated process of hydrologic management of the subsurface which has rendered the process uneconomical.
However, notwithstanding the teachings of the prior art, there has not been shown a method of remediating a site in a controlled manner of poorly biodegradable organics, particularly dissolved chlorinated solvents without vacuum extraction, which is adapted to the specific site and at an economical cost. The present invention accomplishes this by employing microporous diffusers injecting duo-gas bubbles into aquifer regions to encourage biodegradation of leachate plumes which contain biodegradable organics which overcomes at least some of the disadvantages of prior art.